The invention relates to an actuation device for a passenger protection device in a motor vehicle, in particular for an inflatable impact protection cushion (airbag).
Actuation devices for passenger protection devices in a motor vehicle, e.g. belt tensioner or airbag systems, are known from the German Patent No. DE 4102275 C1. As an actuation element, such actuation devices have a low-value resistor wire in an ignition chamber, as well as a detonator which is ignited in the event of a sufficient temperature rise or when the resistor wire melts.
The German published Patent Application No. DE 4429175 A1 discloses an actuation device with a housing made of a metal alloy and with an adapter ring which is inserted in the housing and in which a glass insulator is located. Contact pins, whose ends project into the ignition chamber and meet the front side of the insulator and are connected to a welded-on resistor wire which functions as an actuation element, are sealed into this insulator.
In the known actuation device, the ends of the contact pins sealed into the electrically insulating glass must first be surface-ground with the front side of the glass block so that the resistor wire is positioned cleanly on the glass. Otherwise damage to the welded-on resistor wire cannot be avoided due to the pressure of the priming layers of solid pyrotechnical material which is filled into the ignition chamber under high pressure.
Furthermore, this design has the disadvantage that the detonator may become detached from the glass body in the event of shaking movements, knocks or temperature fluctuations through the forces that can then occur, so that contact to the resistor wire deteriorates or is even interrupted. In such a case, the detonator can no longer be ignited reliably.
Furthermore, depending on the defined value of the actuation signal of the actuating and monitoring electronics, a suitable resistance value must be used for the resistor wire, which in turn results in a differing length of the resistor wire and thus in a differing distance between the two contact pins within the ignition chamber. Consequently the contact pins, which are usually at a distance from each other permanently defined by the plug of the monitoring electronics, must be bent to different degrees in order to guarantee this necessary gap in the housing.
From International Patent Publication No. WO 95/11421, an actuation device is known which in principle is designed in a similar way to the above-mentioned device in accordance with DE 44 29 175 A1 and which is assumed to be the latest state of technology as formulated in patent claim 1. Here two nail-shaped contact pins are inserted in an electrically insulating plastic or rubber material, with the flat heads of the contact pins being in contact with the upper side of the plastic material. The resistor wire is intended to be positioned between the heads; the primary detonator is mounted on this wire, and this detonator is in turn in contact with the remaining detonator in the ignition chamber.
In practice, such an actuation device is not reliable in use, since in particular the sealing problems between the plastic material and the nail heads are considerable. Moreover, here there is the problem that shaking movements, knocks or temperature fluctuations acting on the actuation device can cause the resistor wire and the detonator to lose contact with each other, so that reliable actuation is no longer guaranteed.
A further problem in such actuation devices is overvoltage, which can lead to incorrect actuation. For this reason, this overvoltage must be discharged, and for this purpose a specified spark gap is generally created as an overvoltage arrester. The specified spark gap is the shortest distance between two parts with differing conductivity within the actuation device.
In the actuation device in accordance with the above-mentioned DE 4429175 Al, a spark gap is formed by a conductive ring provided for this purpose, which leaves a gap free to the contact pins that transmit the signals of the actuating and monitoring electronics. Any sparks are thus transmitted from the housing to the contact pins and not to the actuating wire.
It has turned out, however, that in the event of overvoltage of only several kilovolts (kV) this overvoltage cannot be discharged via the spark gap, so that the resistor wire of the actuation device melts and the actuation device is triggered.
Moreover, the installation of the conductive ring or equivalent elements to form a spark gap requires further sealing measures and expensive manufacturing operations, while at the same time enlarging the overall dimensions of the device.
A principal object of the present invention is therefore to create an actuation device for a passenger protection device in a motor vehicle whose production is simple and less elaborate, and in particular does not require the operation of surface-grinding the contact pins.
The invention is also based on the task of creating an actuation device which can be adapted easily, without involving additional work and expense, to the values defined by the manufacturers of the monitoring electronics.
A further objective of the present invention is to equip the actuation device with an integrated overvoltage arrester requiring no additional elements or manufacturing operations.
In accordance with the invention, these tasks are achieved by providing contact pins which are shaped like nails, having one neck and one head each. The heads of the contact pins are caused to project into the ignition chamber and the resistor wire is connected between the heads of the two pins. Finally, the detonator, which is free-flowing during the manufacture of the device, surrounds the heads of the contact pins and the resistor wire and subsequently solidifies.
In accordance with the invention, the cost of producing the actuation device is reduced through the use of nail-shaped contact pins projecting into the ignition chamber, on the heads of which a resistor wire of the required length is attached, preferably welded on. In order to be able to guarantee the stability and durability of the device, the housing is filled with a detonator which is initially fluid and surrounds the heads of the contact pins and the resistor wire, and subsequently solidifies. Such detonators are known: The German patent No. DE 4319919 C1 describes detonators and explosives which are free-flowing during manufacture and which thereafter solidify.
As a result of these measures, isotropic pressure acts on the wire, thus ruling out the possibility of any damage caused by pressure. Furthermore, the detonator is anchored to the heads of the contact pins, so that even in the event of expansion and stretching of the detonator due to temperature fluctuations, vibrations in the actuation devices or knocks on them cannot detach the detonator; this guarantees that actuation is always reliably effected. Temperature tests in which the actuation device was exposed to temperature fluctuations between +110xc2x0 C. and xe2x88x9240xc2x0 C., as well as vibration tests, have confirmed this.
Surface-grinding of the contact pins with the insulator is not necessary either, which simplifies the manufacture of the actuation device significantly.
Pyrotechnical mixtures with a binder, which are initially fluid and subsequently solidify, are preferred.
In the design in accordance with invention, it is not necessary to attach the ends of the resistor wire to the edges of the pin heads, since, as experiments have shown, the resistance surprisingly depends essentially only on the length of the wire between the points of attachment, so that the wire can be attached to any point on the upper side of the head of the nail. This fact results in a simple adaptation of the resistance value of the resistor wire to the values of the actuation signals defined by the manufacturers of the actuating and monitoring electronics by varying the length of the resistor wire and thus the position of the points of attachment on the heads of the pins. This means that it is not necessary to vary the gap between the contact pins in the ignition chamber, e.g. by bending the contact pins to different angles. On the contrary, these can be straight and have a constant distance from one another. The diameters of the heads of the contact pins are dimensioned in such a way that the entire value range for the resistance of the resistor wire is covered for monitoring electronics supplied by various manufacturers.
Furthermore, in accordance with the invention, instead of the almost point-shaped spark gaps known so far, a relatively large-surfaced or linear spark gap is provided as an overvoltage arrester. It has turned out that in the event of higher overvoltage values, several sparks can also flash over at the same time, and the overvoltage is discharged reliably without the actuation device being triggered. On the basis of the geometry and arrangement of the elements of the actuation device, an additional element does not have to be installed for this purpose. In accordance with the invention, the spark gap is preferably achieved by surrounding the contact pins with an electrically conductive extension of the housing, spanning a considerable length of the necks of the contact pins. This length is selected so that it is, for example, approximately comparable with the circumference of the contact pins. The internal wall of the extension is preferably roughened, for example it is equipped with a thread. It has turned out that when overvoltage occurs, this design also allows several sparks to flash over simultaneously.
As explained above, the bending of the contact pins and the surface-grinding of the pins with the insulation glass is avoided through the present invention. The result is a considerable reduction in the manufacturing effort and manufacturing costs involved, and simple universal adaptability to the requirements of the respective manufacturers of the actuating and monitoring electronics. A further reduction in the cost and effort involved in manufacturing is effected by the geometry-specific integrated overvoltage arrester in accordance with the invention.
The design in accordance with the invention complies with the requirements of the function guarantee for at least ten years, and is gas-tight and in particular, helium-tight.
In the following, the invention shall be explained in greater detail on the basis of an embodiment with reference being made to the accompanying drawing, in which a sectional view of an actuation device with an integrated overvoltage arrester in accordance with the present invention is shown.